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  • 1990-1994  (19)
  • 1985-1989  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Microwave testing of high-Tc based direct current to a single flux quantum converter (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5996-6000 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Design, simulation, and experimental investigations of a direct current to a single flux quantum converter loaded with a Josephson transmission line and driven by an external 70 GHz microwave oscillator are reported. The test circuit includes nine YBaCuO Josephson junctions aligned on the grain boundary of a 0°–32° asymmetric Y-ZrO2 bicrystal substrate. The performance of such converters is important for the development of the fast Josephson samplers required for testing of high-Tc rapid single flux quantum circuits in high-speed digital superconducting electronics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358383
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  • 2
    Electronic Resource
    Electronic Resource
    Growth and properties of YBa2Cu3O7−x/(SrTiO3/PrGaO3)/YBa2Cu3O7−x trilayers: Optimization of the insulation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 827-834 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: YBa2Cu3O7−x/insulator/YBa2Cu3O7−x trilayers with a single PrGaO3 (PGO) layer or a SrTiO3 (STO)/PGO multilayer as the insulator were prepared by laser deposition. The PGO layers contained pinholes extending down to the bottom layer, causing superconducting microshorts. The pinholes were eliminated by introducing thin STO films, both as buffer layers and in the PGO itself. Insulation resistivity values of 2×109 Ω cm were measured at 77 K for areas up to 1500 μm2 in these trilayers. For larger areas the insulation decreased by orders of magnitude. This was caused by local disruption of the insulator layer, possibly induced by contaminations or defects in the substrate. The particles observed on the bottom layer were in general continuously covered by the multilayer insulator, and did not affect the insulation. The high-quality insulator layer was found to limit the oxidation of the bottom layer, due to a slower rate of oxygen diffusion. The structure of the STO/PGO layers depended on the thickness of the individual films. Voids started to form in the PGO above a critical thickness of 40 nm. The voids lowered the dielectric constant of the insulator, and a value of 18.5±4.5 was measured at room temperature for a STO/PGO multilayer insulator. The voids could be eliminated by decreasing the thickness of the individual PGO films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356436
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Bicrystal junctions and superconducting quantum interference devices in YBa2Cu3O7 thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7972-7977 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions and superconducting quantum interference devices (SQUIDs) were made by depositing thin films of YBa2Cu3O7 on bicrystal substrates of Y-ZrO2 and SrTiO3. The critical current density of the junctions at 77 K could be adjusted from 100 to 106 A/cm2 by selecting bicrystals with misorientation angles θ from 45° to 0°. Current-voltage curves from junctions with θ(approximately-greater-than)22° followed the resistively shunted junction model with noise rounding close to the transition temperature. The response of the critical current to magnetic fields was Fraunhofer-like and the width (w) dependence was 1/w2 due to flux focusing effects. Shapiro steps under microwave radiation were observed. SQUIDs based on these junctions had energy resolutions at 77 K down to 8.6×10−30 J/Hz and a 10 Hz flux noise level down to 1.5×10−9 Φ20/Hz at 85 K. A SQUID of the Ketchen design with a flux focusing washer had a magnetic field sensitivity of 15 pT/(square root of)Hz at 77 K. The temperature dependence of the voltage modulation depth close to TC was examined and found to be in agreement with theory [K. Enpuku, Y. Shimomura, and T. Kisu, J. Appl. Phys. 73, 7929 (1993)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356559
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  • 4
    Electronic Resource
    Electronic Resource
    YBa2Cu3O7−x films on yttria-stabilized ZrO2 substrates: Influence of the substrate morphology (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7958-7965 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: c-axis-oriented YBa2Cu3O7−x (YBCO) thin films were laser deposited on (001) yttria-stabilized ZrO2 (YSZ) substrates with different surface morphologies. The in-plane orientation of the films on smooth substrates was sensitive to the deposition conditions, often resulting in mixed orientations. However, a strongly dominating [110]YBCO//[110]YSZ orientation was obtained at a deposition temperature of 770 °C. Films on substrates with surface steps, induced by depositing a homoepitaxial buffer layer or by thermally annealing the substrate, had a [110]YBCO//[100]YSZ orientation when deposited at the same temperature. It was concluded that the [110]YBCO//[100]YSZ orientation was promoted by a graphoepitaxial mechanism. Films prepared under identical conditions on smooth and stepped substrates grew with extended c axes on the former. It is proposed that the extension can be induced by disorder, invoked by a low oxygen pressure and a low density of adsorption sites. The disorder may be eliminated by either an increase of the oxygen pressure or an increase of the density of adsorption sites in the form of steps. The film microstructure influenced the microwave surface resistance, which was similar for films with one exclusive in-plane orientation and higher for films with mixed orientations. The films on the stepped surfaces had superior superconducting properties; inductive measurements gave a Tconset of 88 K, a ΔT(90%–10%)c of 0.2 K, and the transport jc was 1.5×106 A/cm2 at 83 K, for films on substrates with homoepitaxial buffer layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356557
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  • 5
    Electronic Resource
    Electronic Resource
    High-frequency limits of superconducting tunnel junction mixers (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4482-4498 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated high-frequency limits of superconducting quasiparticle mixers from experiments on Al/Al-oxide-In/Al (or Ag) tunnel junctions, and from calculations based on Tucker's quantum theory of mixing (QTM). The small superconducting energy gap of Al enabled us to study mixer performance at around the junction gap frequency, fg =(Δ1+Δ2)/h≈87 GHz, of superconductor-insulator-superconductor (SIS) mixers, and at twice the junction gap frequency for S-I-normal metal (SIN) mixers ( fg =Δ1/h) with available millimeter wave sources. Because of the low transition temperature of Al (Tc ≈1.3 K), a dilution refrigerator was used for providing temperatures below 1 K. The best mixer conversion efficiency was obtained for a low-resistance (∼34 Ω) six-junction array SIS mixer operated at f/fg ≈1 (in this case 73 GHz). The coupled single sideband conversion gain (with no image rejection) was −13.8 dB and the available conversion gain was estimated to −8.4 dB. Complicating nonequilibrium phenomena made it difficult to compare the performance of these relatively high-current-density mixers to the QTM. However, good agreement between calculated and corresponding measured conversion efficiencies and dynamic resistance values was obtained for the low-current-density mixers. Noise due to switching between rf-induced Josephson steps and interference from Josephson mixing could be quenched by a magnetic field. Several high-frequency limits are considered in this paper (such as Josephson switching noise, nonequilibrium phenomena, pair breaking, and energy gap limitations). Our results indicate that submillimeter wave SIS mixer receivers are likely to perform well, at least up to their gap frequencies, i.e., the THz region for large gap superconductors. Our QTM calculations showed that conversion gain larger than unity should be possible up to twice the gap frequency. Above this frequency the conversion loss will increase rapidly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339038
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  • 6
    Electronic Resource
    Electronic Resource
    Low-noise Josephson parametric amplification and oscillations at 9 GHz (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5234-5243 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the performance of a resistive rf SQUID as a 9 GHz parametric amplifier and oscillator. It was coupled to a low impedance microstrip transformer. Stable Josephson oscillations were obtained for βLQ =2eI0ZL/hf 〈1.1–1.8. Oscillation linewidth (830 kHz) and output power (−74 dBm) were measured. The four-photon internally pumped amplifier produced large single sideband (ssb) noise temperatures, typically around 50 K, due to the broad flanks of the pump. The best performance was achieved in the three- and four-photon externally pumped modes. Both modes gave signal gains of about 10 dB and negligible noise power contributions. A hot/cold measurement on the four-photon amplifier yielded Gdsb =13 dB (dsb=double sideband) and Tdsb =3±4 K over a bandwidth of 310 MHz. For larger values of βLQ , subharmonics 1/2 and 1/3, as well as noninteger "excitations'' of the Josephson oscillation, were observed. The subharmonic oscillations were not tunable in frequency with unchanged linewidth. Amplification close to an excitation also produced gain but with ssb noise temperatures of ∼20 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342409
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    A millimeter wave Josephson mixer employing a high-Tc GdBaCuO point contact (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4923-4926 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated a Josephson effect heterodyne mixer for the millimeter wave band employing high-Tc GdBaCuO point contacts. Mixer performance was in qualitative agreement with theory. A mixing response was observed up to 55 K, the highest operating temperature achieved for such a device to date. The voltage separation of rf-induced steps gave a value of h/2e=2.08×10−15 V s which is in excellent agreement with the value expected for Cooper pairs. In addition, the temperature dependence of the I0R product was found to agree with Bardeen–Cooper–Schrieffer theory in the weak coupling limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339003
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  • 8
    Electronic Resource
    Electronic Resource
    Growth and properties of a multilayer system based on Y1Ba2Cu3Ox and amorphous Y-ZrO2 (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 199-202 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth of c-axis oriented Y1Ba2Cu3Ox thin films on an amorphous buffer layer of Y-ZrO2, deposited on sapphire substrates, was investigated. Both films were grown by a pulsed laser deposition technique. A strong correlation was observed between the properties of Y1Ba2Cu3Ox and the thickness of the buffer layer. A Tc of 89 K was obtained for an optimal buffer layer thickness of 9 nm. A model that adequately describes the film growth process was developed. A multilayer system of Y1Ba2Cu3Ox and amorphous Y-ZrO2 was grown and a Tc of 87 K for the upper c-axis oriented layer was measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352157
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  • 9
    Electronic Resource
    Electronic Resource
    Design of multiloop input circuits for high-Tc superconducting quantum interference magnetometers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1918-1935 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique is developed for the design of input circuits of superconducting quantum interference devices (SQUIDs) including those based on high transition temperature (Tc) superconductors. A multitransformer SQUID circuit is reduced to a single-loop one with effective values of its loop inductance and applied flux. A numerical model of a multitransformer magnetometer is formed and analyzed. The planar transformer coupling coefficient is evaluated. The multitransformer SQUID structures as a whole are optimized with respect to their performance, taking into account the limits set by fabrication technology. Three gradiometer-type device designs are discussed. The most complex SQUID treated is a second-order gradiometer for magnetoencephalography use which needs only a two superconducting films technology to be realized. Designs are based on available high-Tc superconductor technology. Very competitive performance with high energy resolution and magnetic-field gradient sensitivity is predicted at nitrogen temperature using a multitransformer coupling circuit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351667
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  • 10
    Electronic Resource
    Electronic Resource
    Linewidth measurements of Josephson flux-flow oscillators in the band 280–330 GHz (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3195-3197 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An integrated receiver consisting of two Josephson flux-flow oscillators and a superconductor-insulator-superconductor (SIS) mixer has been used to measure the linewidth of the oscillators. The oscillators are coupled to the SIS mixer using two centerfed interdigital capacitors, one of which with a fairly weak (−20 dB) coupling. By biasing the two oscillators (a few microvolt apart) on their velocity matching steps, the two resulting oscillations (280–330 GHz) were mixed in the SIS mixer. The difference frequency was amplified and detected on a spectrum analyzer. The combined linewidth of the two oscillators was 2.1 MHz throughout the band. The calculated available power incident on the SIS mixer was 430 nW at 320 GHz. The rf power from the oscillators, which could be tuned by changing the current bias, is high enough to pump the SIS mixer optimally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109127
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